.\"
.\" Copyright (c) 2001 Dima Dorfman.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD: src/lib/libc/gen/getpeereid.3,v 1.6 2002/12/18 10:13:54 ru Exp $
.\"
.Dd July 15, 2001
.Dt GETPEEREID 3
.Os
.Sh NAME
.Nm getpeereid
.Nd get the effective credentials of a UNIX-domain peer
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In unistd.h
.Ft int
.Fn getpeereid "int s" "uid_t *euid" "gid_t *egid"
.Sh DESCRIPTION
The
.Fn getpeereid
function returns the effective user and group IDs of the
peer connected to a
.Ux Ns -domain
socket.
The argument
.Fa s
must be a
.Ux Ns -domain
socket
.Pq Xr unix 4
of type
.Dv SOCK_STREAM
on which either
.Xr connect 2
or
.Xr listen 2
have been called.
The effective used ID is placed in
.Fa euid ,
and the effective group ID in
.Fa egid .
.Pp
The credentials returned to the
.Xr listen 2
caller are those of its peer at the time it called
.Xr connect 2 ;
the credentials returned to the
.Xr connect 2
caller are those of its peer at the time it called
.Xr listen 2 .
This mechanism is reliable; there is no way for either side to influence
the credentials returned to its peer except by calling the appropriate
system call (i.e., either
.Xr connect 2
or
.Xr listen 2 )
under different effective credentials.
.Pp
One common use of this routine is for a
.Ux Ns -domain
server
to verify the credentials of its client.
Likewise, the client can verify the credentials of the server.
.Sh IMPLEMENTATION NOTES
On
.Fx ,
.Fn getpeereid
is implemented in terms of the
.Dv LOCAL_PEERCRED
.Xr unix 4
socket option.
.Sh RETURN VALUES
.Rv -std getpeereid
.Sh ERRORS
The
.Fn getpeereid
function
fails if:
.Bl -tag -width Er
.It Bq Er EBADF
The argument
.Fa s
is not a valid descriptor.
.It Bq Er ENOTSOCK
The argument
.Fa s
is a file, not a socket.
.It Bq Er ENOTCONN
The argument
.Fa s
does not refer to a socket on which
.Xr connect 2
or
.Xr listen 2
have been called.
.It Bq Er EINVAL
The argument
.Fa s
does not refer to a socket of type
.Dv SOCK_STREAM ,
or the kernel returned invalid data.
.El
.Sh SEE ALSO
.Xr connect 2 ,
.Xr getpeername 2 ,
.Xr getsockname 2 ,
.Xr getsockopt 2 ,
.Xr listen 2 ,
.Xr unix 4
.Sh HISTORY
The
.Fn getpeereid
function appeared in
.Fx 4.6 .